AR stands for Accessible Radiation. The laser class of the projector is specified according to the Accessible Radiation (AR). It is the maximum possible emission that may exit the laser aperture. Limit values are given in IEC 60825-1 „Safety of laser products, part 1".
The MPE in contrast to the AR references the laser immission in public area - which is completely different!
Please also see the MPE FAQ for details.